A United Nations inquiry into the assassination of former Pakistani PM Benazir Bhutto begins on Wednesday. It is headed by Chile's ambassador to the UN, Heraldo Munoz, and includes a former Indonesian attorney general and a former senior Irish police officer. The inquiry will last six months and investigate the "facts and circumstances" of Ms Bhutto's killing. She was killed in December 2007 as she left a rally of her Pakistan People's Party (PPP) supporters in Rawalpindi. The three-member inquiry team will arrive in Pakistan later this month and submit its report to the UN Secretary General in six months, reports say. Apart from Mr Munoz, the other members of the probe team are Marzuki Darusman, the former Indonesian attorney-general, and Peter Fitzgerald, who had headed an early inquiry into the assassination of former Lebanese prime minister Rafik Hariri. Pakistan's Interior Minister, Rehman Malik, told the BBC that his government thought the UN investigation was necessary to find out who was behind the attack. "We want to know who was behind this, who had conspired it, who has financed it. And we think this was a big international conspiracy," he said. "Obviously, there might be some actors within in Pakistan or within region, but we want really expose the whole conspiracy, because we think that this was a kind of a beginning of an attempt to Balkanise Pakistan." These are challenging times in Pakistan to carry out such an investigation, says the BBC's World Affairs correspondent Mike Wooldridge in Islamabad. That is not least because the Pakistan Taliban leader Baitullah Mehsud, accused by the last government here of being behind the assassination, is the target of a two-month-old military offensive and his militant network has hit back with retaliatory suicide attacks. The Taliban commander has denied having anything to do with Ms Bhutto's killing. 'Rogue elements' Her assassination left questions unresolved for many people here, but especially her own party, which is now in government. After she had narrowly escaped a double suicide bombing on the day of her arrival back in Pakistan from self-imposed exile in October 2007, she accused what she called "enemies" and "rogue elements" in the then-government led by President Pervez Musharraf and in the intelligence agencies of plotting to kill her. The UN inquiry cannot itself launch criminal proceedings, but can apparently apportion blame if it chooses to do so. Officials say the inquiry will work "fairly discreetly". Former Pakistani President Pervez Musharraf had blamed an al-Qaeda-linked militant for the attack and refused to seek a UN inquiry. He invited police from London's Scotland Yard to assist in the inquiry into her death. In their report the British detectives said they believed she died due to a severe head injury sustained as a consequence of a bomb blast. The Pakistani investigation into her death concluded that a lone attacker fired shots at Ms Bhutto before detonating explosives, but said that bullets were not the cause of death.